1. Field of the Invention
The present invention relates to a method of generating three-dimensional image data on the basis of a plurality of two-dimensional image data that are obtained at different time, and further relates to an ultrasonic diagnostic apparatus for medical diagnosis using the method of generating image data.
2. Description of a Related Art
Conventionally, in order to obtain three-dimensional images using ultrasonic diagnostic apparatus, a plurality of cross-sectional two-dimensional images are collected, and the three-dimensional images are composed thereof. These two-dimensional cross-sectional images are obtained by synthesizing a plurality of picture element data, which were collected in time series by scanning an object by using a one-dimensional sensor array with a positioning sensor, and then, three-dimensional data is obtained by interpolating between cross sections on the basis of a plurality of two-dimensional cross-sectional images.
According to this method, however, there are time lags in the scanning direction of the sensor array, and therefore, cross-sectional images at different time are synthesized. Also, since the images are synthesized on the basis of information obtained by monitoring a position of the sensor, the composite images become unclear. Thus, this method is not suitable for synthesizing images of a living body such as in an ultrasonic diagnostic apparatus.
In order to solve the problem, it is desirable to use a two-dimensional sensor array for obtaining three-dimensional images. For example, it may be considered to collect ultrasonic signals as optical two-dimensional images by using an optical fiber array. According to this method, a plurality of two-dimensional data can be sequentially collected on the basis of ultrasonic signals incident on the two-dimensional sensor array when a predetermined time has passed after an ultrasonic wave is transmitted. However, the two-dimensional data includes all incident ultrasonic signals when the predetermined time has passed after transmitting, and therefore, it would not represent data about a specific point in three-dimensional space if not adjusted.
In the meantime, a document titled xe2x80x9cA principle of three-dimensional displayxe2x80x9d written by Tsuyoshi Mochizuki is reported in xe2x80x9cClinical Radiationxe2x80x9d Vol. 43 No. 11 (1998). In this document, it is reported that conventional methods of collecting data by changing sections scanned by ultrasonic waves take a large quantity of time before the whole data aggregate is obtained, and therefore, in the case where a scanned object is a moving one, a precise image cannot be obtained. The document refers to a data collection method using a moving two-dimensional piezoelectric transducer array as one of possible solutions, and also it refers to a method of displaying a surface and internal information of an object simultaneously as a direct method. However, it mentions that hardware and signal processing need a large scale of operation at the present time.
The present invention has been accomplished in view of such problems as mentioned above. The first object of the present invention is to provide a method of generating three-dimensional images on the basis of a plurality of two-dimensional data obtained at different time by using a two-dimensional sensor array. The second object of the present invention is to provide an ultrasonic diagnostic apparatus using such a method as above.
In order to solve the above problem, a method of generating three-dimensional image data by transmitting beams to an object to be measured by using transmitting means and detecting beams reflected from the object by using a two-dimensional sensor array including a plurality of sensors, according to the present invention comprises the steps of: (a) sequentially storing detection signals obtained by the plurality of sensors during a predetermined period of time after transmission; (b) obtaining image data about at least one measured point included in the object on the basis of a detection signal output from at least one of the plurality of sensors at a time point obtained from relationship between a distance from the transmitting means to at least one of the plurality of sensors through the at least one measured point and a transmission velocity of the beams passing through the object; and (c) obtaining image data by repeating step (b) while changing the time point.
Also, an ultrasonic diagnostic apparatus according to the present invention comprises: a driving signal generating means for generating driving signals; ultrasonic transmitting means for transmitting ultrasonic waves to an object to be measured on the basis of driving signals generated by the driving signal generating means; a two-dimensional sensor array including a plurality of sensors for detecting ultrasonic waves reflected from the object to generate detection signals; signal processing means for processing the detection signals obtained by the plurality of sensors; control means for controlling action timing of the driving signal generating circuit and the signal processing means; storage means for storing the detection signals output from the signal processing means during a predetermined period after transmission; and image processing means for obtaining three-dimensional image data on the basis of the detection signals output from the plurality of sensors at respective time points obtained from relationship between respective distances from the ultrasonic transmitting means to respective sensors through respective measured points and a transmission velocity of the ultrasonic waves passing through the object.
According to the present invention, three-dimensional image data can be generated on the basis of a plurality of two-dimensional image data sequentially obtained at the same sensor position by using a two-dimensional sensor array. Accordingly, clear three-dimensional images can be obtained even in the ultrasonic diagnostic apparatus used for an object of a living body.